The present invention relates to a fast atom beam source for producing a fast atom beam that is used for sputtering, for example.
FIG. 4 shows the arrangement of a fast atom beam source which has heretofore been known. In the figure, reference numeral 1 denotes a hollow, cylindrical casing having a central portion with an enlarged diameter, 2 a circular filament for emitting thermal electrons, 3 an ion beam 4 a fast atom beam, 5 a power supply for heating the filament 2, 6 a DC bias power supply, and 7 an ion source.
The circular filament 2 is incorporated in the enlarged-diameter central portion of the casing 1. The filament 2 is disposed in such a manner that the center of its circular configuration is coincident with the axis of the casing 1. The filament 2 is connected with the heating power supply 5. p The DC bias power supply 6 is connected between the casing 1 and the filament 2 to bias the casing 1 to a potential which is several V lower than the potential of the filament 2.
The ion source 7 is disposed so that the ion beam 3 emitted therefrom enters the inside of the casing 1.
It should be noted that the constituent elements, exclusive of the power supplies 5 and 6, are accommodated in a vacuum container (not shown).
The fast atom beam source thus arranged operates as follows.
When the filament 2 is heated by the heating power supply 5, a large number of thermal electrons are emitted therefrom. The thermal electrons are repelled by the wall of the casing 1 biased to a potential lower than the potential of the filament 2, so that the thermal electrons concentrate near the axis of the casing 1, thus forming a high density electron cloud there. When the ion beam 3 that is emitted from the ion source 7 enters the electron cloud, collision and recombination between ions and electrons occur, so that the ion beam 3 is converted into a fast atom beam 4.
In the collision between ions and electrons that occur in the above process, since the mass of electrons is much smaller than the mass of ions, the ions deliver the kinetic energy to the atoms without a substantial loss, thus producing a fast atom beam 4.
However, in the conventional fast atom beam source with the above-described arrangement, the relative velocity between the electrons in the electron cloud and the ions in the ion beam is large and the recombination cross section of ions and electrons is small, so that it is difficult to produce a fast atom beam efficiently.